WLAN Traffic Offload in LTE

In most modern cellular mobile phones, WLAN is an integral part. However, in today’s implementations the cellular standards and WLAN are completely independent. The Internet is accessed either via LTE and the attached evolved packet core (EPC) or directly using WLAN. The access technology is switched manually, requiring separate authentication. Service continuity cannot be supported because a new connection is established and the IP protocol stack is cleared.

Specifications are underway in merging both technologies in a way that the user equipment (UE) can access the EPC directly over the WLAN interface. This will allow services to be seamlessly transferred between 3GPP and WLAN, maintaining the ongoing sessions so that users do not perceive the handover. This integration enhances coverage because the UE can automatically select the best available access technology. The widely used manual authentications in WLAN networks are replaced by a seamless automatic authentication over the 3GPP AAA server using USIM card credentials. In addition, the cellular network load towards the air interface can be relieved in case of heavy traffic.

In order to implement this kind of offload, the WLAN system connects to the PDN-GW, either directly in a trusted access, or via an additional node, the ePDG, in a nontrusted access. The ePDG is under full EPC network operator control and thus enables the provision of all necessary security functionalities. The difference between trusted and nontrusted access is mainly a business decision and not technology driven. Its usage depends on the business relationship between the mobile network and the WLAN network operators.

According to the current state of the specification, the offload decision is taken by the UE, optionally with support from the access network discovery and selection function (ANDSF). The ANDSF provides policies to the UE for intersystem mobility and routing, as well as access network discovery. Investigations in 3GPP RAN are studying the possibility of transferring the offload control to the network and thereby enable the operator to provide the best quality for the connection. Rohde & Schwarz is closely following this development and will provide for each step highly sophisticated test and measurement solutions.

Resources for WLAN Traffic Offload in LTE

Products for WLAN Traffic Offload in LTE

  • R&S®CMW500
    • Universal tester for testing the air interface of wireless devices, supporting all relevant wireless standards, e.g. GSM, UMTS/HSPA+, CDMA2000® and LTE as well as associated inter-RAT messages
    • Simultaneous WLAN and LTE signaling in one box
    • IP protocol stack emulation with access to LTE and WLAN
    • Internal IMS server and interface for external IMS server connection
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